The extruder is the predominant machine of
an extrusion plant.
It allows the material to reach
the required break-down and to flow through the
die, which is firmly assembled to its head. Raw
rubber is normally cut in stripes and feeds the
internal screw of the extruder, which transfer
energy to the rubber itself and makes it
machinable from the die into the desired profile.
The most important parameters of temperature
and internal pressure are ruled by PLC and
controlled by skilled personnel.
The production lines of Tecnoextr Spa actually
include extruders both horizontal than vertical, for
the manufacturing of a wide range of different
profiles and tubes, with diameters from a few tenth
to around 130 mm.
Even if it is required just an easy machining to
get them, the dies must be carefully designed
and, if necessary, modified for being tuned.
First of all, extreme care and a long experience
must be dedicated to designing the orifice.
The extrusion process of rubber materials avails
itself of the following components:
- Curing oven
- Cooling bath
- Postcuring ovene
Extrusions dies for rubber are usually machined
by electroerosion from steel discs, having diameter
and thickness as a function of the rubber material
and of the kind of profile and, in case of hollow
shape, cores supported on the slotted disc with a
A rubber uncured extruded profile flowing out
from the die is free to varying its own geometry,
because after being piped under a growing
pressure on the screw, leaving the die the
pressure drops to relative zero.
Because of this rush of pressure, which leads to
swelling due to the increase of material entropy at
a high temperature and low viscosity, the
extrudate may collapse and vary its shape under
Vulcanization, which implies a rapid raise of
viscosity, takes place and starts in the oven, so
between die and oven the extrudate doesn’t have
to vary its own geometry or, at least, it has to be
predicted and controlled.
All this makes clearer that quite often the
geometry of the die orifice is very different if
compared with the section of the desired
This is a typical case of reverse
engineering, when one has to determine a
system to producing the wished result starting
from the result itself: the extruded profile
according a drawing.
extruder head and locking device
It has to be evidenced that all the dies must be
developed and tuned according to the material of
the profile, which may have a certain hardness or
viscosity, and to the profile geometry.
It has to be furthermore remarked that, even if the
orifice geometry one can see on the external side
of the die may be considered as ideal and correct
for a certain profile, the internal side is usually
shaped differently and then eroded step by step in
order to get a uniform material flow in the die land.
For example, it is possible to accelerate the
material flow reducing friction losses dulling the
edges or creating converging sections. On the
contrary one can slow down the flow rate locally
by means of artificial friction losses inserting so
Of course, when possible, it is better to get a
uniform wall thickness of the profile so that a
constant mass flow rate is reached and to avoid
areas thicker than the rest or edges where
material stagnation or cracks may take place.
ref. 16 - isovelocity surfaces on a profile section
The whole wide range of extrusion dies
manufactured by Tecnoextr Spa have been
developed inside the company thanks to a long
experience in this field, so today die design has
become a daily task and the results of this
activities have been valued and called for by the
A few centimeters downstream from the die the
profile is carried on the curing oven belt,
where it crosslinks at controlled temperature
according imposed parameters depending upon
extruded material and profiles geometry.
Soon afterwards, if necessary the profile is
cooled down in water, spooled, cut or punched.
Depending upon the material extruded, the
profiles are postcured in hot air ovens according
specific cycles to completing crosslinking and to
completely releasing additives and vulcanization
Tecnoextr Spa supplies extruded endless profiles
in bundles or spooled over plastic or paperboard
A collection of profiles is showed on the last
pages of the catalogue.
This list, here showed partially, is continuosly
updated and integrated with new articles.
Tecnoextr Spa remains at disposal of his own
customers for further information and to
suggesting the best fitted solution for the
Tecnoextr Spa transform a wide range of rubber
materials, both compact than cellular, into
reliable and carefully manufactured extruded
What it may concern about material performances
is mentioned on tables and graphs in the
introduction area of this catalogue.
information related to our products may be
requested to our technical department, which
remains always at disposal of the customers.
Extruded rubber profiles require a certain
technological cycle of production, similar to what
it is used for other materials, but with a
distinctive difference. What it makes the difference
between rubbers and the rest of the polymers is the
vulcanization process a rubber part has to
withstand before its use.
This process, which implies an irreversible
crosslinking of the molecules, takes place at
atmospheric pressure transfering heat to the
This heat transfer must be gradual and it is
dependent from profile geometry, profile
dimensions and polymer type.
It is evident that, even if one may try to accelerate
the process of vulcanization, it starts and then it
stops the shape variation only after a certain
period, usually some seconds.
Anyhow it is furthermore intuitive that during this
short time the profile is under an unstable
equilibrium of forces and that its shape may
change under its own weight because of the
Termoplastic extruded profiles, on the contrary,
are usually calibrated and this is made possible
because of the absence of vulcanization and so it
is possible to cool them rapidly all over
Tecnoextr Spa manufactures extruded profiles in
conformity to severe standards with
dimensional tolerances mostly according
UNI ISO 3302-1.
According to the above mentioned standard
norm, the suggested class of tolerances for
cross-sectional dimensions of extruded profiles,
except special cases, is the class E2.
Concerning products cut from tubes or cords and
profiles in general, instead, we apply the class L2.
Tecnoextr Spa manufactures even extruded
profiles made in different qualities of cellular
rubbers. Tolerances related to such this kind of
materials haven’t been included in a standard
norm. Because of the difficult prediction of the
material behaviour during manufacturing, due to
an enormous swelling coefficient related to the
amount of blowing agents added in the
Tecnoextr Spa suggests for these materials the
class E3 for cross-sectional dimensions.
However the E2 class is allowed for simplified
geometry like square or circular cross sections.
It is advisable to consult our technical
department for further details and information.
Tecnoextr Spa plays a distinctive role on the
market because of the products quality and of the
technical support to the customersi.
A huge amount of different applications have
been covered by alternative series of products:
- Inflatable seals, which are extruded hollow
profiles joined as closed circles or as opened
frames with vulcanized ends, able to expand
while inflated with compressed air.
- Profiles modelled from uncured extrudate,
usually silicone hoses handmade or vacuum
- Tubes and profiles with moulded ends, usually
tubes with connectors or elbows moulded over
to improve assembling features.
- Seal frames, manufactured from cut profiles
joined by corner moulding or using specific
- O-rings, joined by mouding
or glued from cords or tubes.
- Flat gaskets and hoses cut from tube.
Tecnoextr Spa is certified UNI EN ISO 9002
Quality procedures rule the whole manufacturing
process, from design to deliveries and produce
an efficient pre and post sales service and a
reliable finished product marked distinctively by
competitive prices and by an excellent global
Tecnoextr Spa works at open books with its own
customers. We do not hide our capabilities and
our technologies and their costs, because wÉre
convinced that only a sincere and cooperating
relationship between us and our customers may
completely satisfy them and that this honourable
dealing is recognized.
With regard to that, it follows a useful scheme for
an estimated profile cost calculation, trusting that
it may result even helpful for a first
understanding of the argument.
Of course it would
be impossible to substitute with this simple
mathematical tool our technical and commercial
department while estimating these costs, but
wÉre sure that, even if with some limitation, these
information may result appreciated and helpful.
One can get some helpful suggestion from this
Some materials are more expensive than others
and it is not always true that a cheaper material
would show worser performances.
It depends upon the application required.
Before proceeding to an inquiry evaluate carefully
the whole application, not only the extruded
profile and choose first a material with the best
ratio between price and performance.
In case of doubts our technical department is
always at your disposal.
Do not oversize unuselessly an extruded profile.
The bigger the cross section, the higher the
weight per linear unit and the higher the cost due
to the material. Furthermore, usually increasing
the weight per linear unit the extrusion velocity
ratio lowers and so the process costs raise.
If possible adopt profiles with a constant wall
Each sensible variation of the wall thickness
along the cross section implies mass flow
All this afflict the extrusion velocity ratio, which
has to be lowered with a consequent raise of the
An extruded profile with a complex geometry
often requires the operator being constantly close
to the extruder controling the process. In case of
simple profiles this may be avoided, because a
single operator may govern more than one
extruder, with a consequent reduction of costs.
A simple slotted die for a compact profile is
A special die for an hollow profile is usually more
Increasing the number of cavities in a profile the
die cost grows and the weight per linear unit of
the profile decreases.
Try to evaluate if it is the case to invest money for
tools, a multicavity die, o if it is better a higher
unit weight respect to what is possible in theory.
Small batches of an extruded profile
manufactured in a certain number of steps for a
certain total amount of meters cost a lot more
than a single batch, because of the succession of
stopped sessions and repeated machine set up.
Each secondary operation has its own cost.
Verify if postcuring, cut, punching or surface
treatment are necessary.
To eliminate or substitute one of these operations
may result possible and consequently